In recent years, with the spread of virtual networks or Internet of things (IoT), network traffic has been increasing steadily. In order to grasp whether a managed network is operating properly, a network operator periodically collects traffic information, and when any abnormality (e.g., sudden increase or sudden decrease in traffic) occurs, the network operator is required to quickly detect the abnormality.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication Nos. 2013-150083 and 2011-244098.